/*
* Copyright 2007 ZXing authors
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
*      http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
using System;
namespace FastReport.Barcode.QRCode
{

    /*/// <summary> <p>This class contains utility methods for performing mathematical operations over
    /// the Galois Field GF(256). Operations use a given primitive polynomial in calculations.</p>
    /// 
    /// <p>Throughout this package, elements of GF(256) are represented as an <code>int</code>
    /// for convenience and speed (but at the cost of memory).
    /// Only the bottom 8 bits are really used.</p>
    /// 
    /// </summary>
    /// <author>  Sean Owen
    /// </author>
    /// <author>www.Redivivus.in (suraj.supekar@redivivus.in) - Ported from ZXING Java Source 
    /// </author>*/
    internal sealed class GF256
    {
        internal GF256Poly Zero
        {
            get
            {
                return zero;
            }

        }
        internal GF256Poly One
        {
            get
            {
                return one;
            }

        }

        //UPGRADE_NOTE: Final was removed from the declaration of 'QR_CODE_FIELD '. "ms-help://MS.VSCC.v80/dv_commoner/local/redirect.htm?index='!DefaultContextWindowIndex'&keyword='jlca1003'"
        public static readonly GF256 QR_CODE_FIELD = new GF256(0x011D); // x^8 + x^4 + x^3 + x^2 + 1

        //UPGRADE_NOTE: Final was removed from the declaration of 'expTable '. "ms-help://MS.VSCC.v80/dv_commoner/local/redirect.htm?index='!DefaultContextWindowIndex'&keyword='jlca1003'"
        private int[] expTable;
        //UPGRADE_NOTE: Final was removed from the declaration of 'logTable '. "ms-help://MS.VSCC.v80/dv_commoner/local/redirect.htm?index='!DefaultContextWindowIndex'&keyword='jlca1003'"
        private int[] logTable;
        //UPGRADE_NOTE: Final was removed from the declaration of 'zero '. "ms-help://MS.VSCC.v80/dv_commoner/local/redirect.htm?index='!DefaultContextWindowIndex'&keyword='jlca1003'"
        private GF256Poly zero;
        //UPGRADE_NOTE: Final was removed from the declaration of 'one '. "ms-help://MS.VSCC.v80/dv_commoner/local/redirect.htm?index='!DefaultContextWindowIndex'&keyword='jlca1003'"
        private GF256Poly one;

        /*/// <summary> Create a representation of GF(256) using the given primitive polynomial.
        /// 
        /// </summary>
        /// <param name="primitive">irreducible polynomial whose coefficients are represented by
        /// the bits of an int, where the least-significant bit represents the constant
        /// coefficient
        /// </param>*/
        private GF256(int primitive)
        {
            expTable = new int[256];
            logTable = new int[256];
            int x = 1;
            for (int i = 0; i < 256; i++)
            {
                expTable[i] = x;
                x <<= 1; // x = x * 2; we're assuming the generator alpha is 2
                if (x >= 0x100)
                {
                    x ^= primitive;
                }
            }
            for (int i = 0; i < 255; i++)
            {
                logTable[expTable[i]] = i;
            }
            // logTable[0] == 0 but this should never be used
            zero = new GF256Poly(this, new int[] { 0 });
            one = new GF256Poly(this, new int[] { 1 });
        }

        /*/// <returns> the monomial representing coefficient * x^degree
        /// </returns>*/
        internal GF256Poly buildMonomial(int degree, int coefficient)
        {
            if (degree < 0)
            {
                throw new System.ArgumentException();
            }
            if (coefficient == 0)
            {
                return zero;
            }
            int[] coefficients = new int[degree + 1];
            coefficients[0] = coefficient;
            return new GF256Poly(this, coefficients);
        }

        /*/// <summary> Implements both addition and subtraction -- they are the same in GF(256).
        /// 
        /// </summary>
        /// <returns> sum/difference of a and b
        /// </returns>*/
        internal static int addOrSubtract(int a, int b)
        {
            return a ^ b;
        }

        /*/// <returns> 2 to the power of a in GF(256)
        /// </returns>*/
        internal int exp(int a)
        {
            return expTable[a];
        }

        /*/// <returns> base 2 log of a in GF(256)
        /// </returns>*/
        internal int log(int a)
        {
            if (a == 0)
            {
                throw new System.ArgumentException();
            }
            return logTable[a];
        }

        /*/// <returns> multiplicative inverse of a
        /// </returns>*/
        internal int inverse(int a)
        {
            if (a == 0)
            {
                throw new System.ArithmeticException();
            }
            return expTable[255 - logTable[a]];
        }

        /*/// <param name="a">
        /// </param>
        /// <param name="b">
        /// </param>
        /// <returns> product of a and b in GF(256)
        /// </returns>*/
        internal int multiply(int a, int b)
        {
            if (a == 0 || b == 0)
            {
                return 0;
            }
            if (a == 1)
            {
                return b;
            }
            if (b == 1)
            {
                return a;
            }
            return expTable[(logTable[a] + logTable[b]) % 255];
        }
    }
}